Purified hydrogen is used in the manufacture of many products including metals, edible fats and oils, and semiconductors and microelectronics. Purified hydrogen is also an important fuel source for many energy conversion devices. For example, many fuel cells use purified hydrogen and an oxidant to produce an electrical potential. A series of interconnected fuel cells is referred to as a fuel cell stack, and this stack may be referred to as a fuel cell system when combined with sources of oxidant and hydrogen gas. Various processes and devices may be used to produce the hydrogen gas that is consumed by the fuel cells.
As used herein, a fuel processing assembly is a device or combination of devices that produces hydrogen gas from one or more feed streams that include one or more feedstocks. Examples of fuel processing assemblies include steam and autothermal reformers, in which the feed stream contains water and a carbon-containing feedstock, such as an alcohol or a hydrocarbon, and partial oxidation and pyrolysis reactors, in which the feed stream is a carbon-containing feedstock. Fuel processors typically operate at elevated temperatures. In endothermic fuel processing reactions, such as in steam reforming fuel processing assemblies, the heat required to heat the fuel processing assembly needs to be provided by a heating assembly, such as a burner, electrical heater or the like. When burners are used to heat the fuel processor, the burners typically utilize a combustible fuel stream, such as a combustible gas or a combustible liquid.
One such hydrogen-producing fuel processing assembly includes a steam reformer, in which hydrogen gas is produced from a feed stream that includes a carbon-containing feedstock and water. Steam reforming is performed at elevated temperatures and pressures, and a steam reformer typically includes a heating assembly that provides heat for the steam reforming reaction. Illustrative but not exclusive uses of the heat include maintaining the reforming catalyst bed at a selected reforming temperature, or temperature range, and vaporizing a liquid feed stream prior to its use to produce hydrogen gas. One type of heating assembly is a burner, in which a combustible fuel stream is combusted with air. Additionally, steam reforming fuel processing assemblies conventionally utilize a fuel stream that has a different composition than the feed stream and which is delivered to, and consumed by, the burner or other heating assembly to heat the steam reformer and/or the feed stream.